1. Field of the Invention
This invention relates to a method and system for performing real-time optical image processing in an image intensifier/television radiographic medical imaging system.
2. Discussion of Background
Typical image intensifier/television (II-TV) systems have a dynamic range of about 1000, which is determined mainly by the TV camera. Within this dynamic range, the signal-to-noise ratio (SNR) varies greatly. At the lower end of the range, the SNR approaches 1:1, and at the higher end it is about 1000:1 for typical TV cameras. Thus, it is advantageous to compress the dynamic range of the image incident on the TV camera and to maintain the signal from the II-TV system near the maximum video level. This is especially important for images having a wide dynamic range or low quantum noise.
Various methods have been introduced for compression of the dynamic range of x-ray images of the thorax. (See, for example J. A. Sorenson, et al., Invest. Radiol. 16, 281 (1981); D. B. Plewes, Med. Phy. 10, 646 (1983); and B. H. Hasegawa, et al., Radiology 159, 537 (1986).) However, these methods are relatively slow and thus are not suitable for dynamic imaging with II-TV systems.
Another group (W. W. Peppler, et al., presented at the Chest Imaging Conference-87, Madison, Wis., 1987), working on a dynamic-range compression method for II-TV systems has reported a technique for producing equalized chest radiographs using an optical beam attenuator which equalizes the light field reaching the TV camera. The optical beam attenuator used was a spatially addressable liquid crystal display (LCD) device which was loaded with a gray-scale transformation of the digitized camera output. It was reported that the benefits of the optical beam attenuator included a potential increase in system DQE (at high dose rates), bit compression, reduced saturation effects and display advantages, as well as the capability of operating at video rates. It was further reported that the optical beam attenuator was capable of reducing dynamic range by a factor of 6.8, but would probably require an additional stage of light amplification.